A particle beam system may be designed, e.g., as an electron beam system or an ion beam system. The use of an electron beam system in particular is already very widespread. An electron beam system is used, e.g., to manufacture nanostructures. An example of an electron beam system is an electron beam microscope, which has been known for a long time, and using which an image of an object may be created. The two known types of electron beam microscopes are the scanning electron microscope and the transmission electron microscope. The scanning electron microscope is used to create high-resolution images of semiconductor structures, biological and mineralogical samples, and other samples.
An electron beam system (also referred to as an electron beam device) such as the scanning electron microscope includes a particle beam generator in the form of an electron beam generator for producing an electron beam, an objective lens for focusing the electron beam on the object, and at least one detector for detecting electrons that are scattered on the object or that are emitted from the object. The electron beam produced by the particle beam generator is focused via the objective lens on the object to be investigated. Using a deflection device, the electron beam is guided in a scanning pattern over the surface of the object to be investigated. The electron beam is therefore scanned over the surface of the object. The electrons of the electron beam interact with the object. As a result of the interaction, electrons, in particular, are emitted from the object surface (“secondary electrons”), or electrons from the electron beam are reflected back (“backscattering electrons”). Secondary electrons and backscattering electrons may be detected using the detector. The detector detects a detector signal depending on the detected secondary electrons and backscattering electrons. The detector signal is used to create an image.
Thermal field emitters or cold field emitters, for example, may be used as the particle beam generators (which are also referred to below as a particle beam source). The use of field emitters of this type has been known for a long time. Cold field emitters that are miniaturized have been used for various applications over the past few years. DE 103 02 794 A1, for example, describes miniaturized electron beam systems having cold field emitters, which are also miniaturized, and which are manufactured using electron beam-induced deposition. In addition, EP 1 186 079 B1 describes a miniaturized electron beam source that operates in the terahertz range.
Cold field emitters have high beam directionality and a low beam energy width. They are therefore particularly well-suited for attaining very small electron beam diameters, thereby making it possible to attain a high resolution. They have the disadvantage, however, that their electron emission current fluctuates over time. The fluctuations over time in the electron emission current become apparent as disturbing light or dark strips in the line grid image when an object is imaged, e.g., in a scanning electron microscope. This is an undesired phenomenon.
Accordingly, it would be desirable to provide a method and a device for producing an image of an object using a particle beam, the method and device being used with a cold field emitter in a manner such that good image quality is always ensured.